Type change during restriction

Hi,

when restricting a complex type, is it actually allowed (at all) to
change the type of an attribute defined at the complex type to be
restricted ?

I am a committer of the XML data binding tool Castor, and one of our
users has presented us with a set of XML schema instances with exactly
such a scenario.

I have been looking at

http://www.w3.org/TR/2004/REC-xmlschema-1-20041028/structures.html

but was not able to find a definitive answer to this question.

Any help appreciated ...

Regards
Werner